1. Field of the Invention
This invention relates to frame based digital communication systems and more particularly to a method for processing frames having a certain size in systems configured for frames having a different size.
2. Description of the Related Art
Digital data is often communicated in frames, which are groups of digital data that are processed together, as will be further described below. Often, it is desired to send or receive frames having a certain size in systems configured for different sized frames. For example, in the IS2000.2-A standard for code division multiple access (CDMA) communications, encoded symbols at a rate of L symbols per frame must be matched with a transmission scheme that processes N symbols per frame, where N is greater than L. In this case, for any one frame, the L symbols are repeated M times, where M is the smallest integer such that ML>N. Then, the ML symbols are reduced to N symbols by deleting (puncturing) P symbols, where P=ML−N. There is no appreciable loss of information since in CDMA, many symbols are redundant to provide robust protection against transmission errors; deleting a few redundant symbols will typically not cause any significant problems, especially if the symbols are far apart.
The above mentioned two stage approach has drawbacks. If complex control logic is not used, then it requires unnecessary additional memory to store the ML symbols; in the worst case, this can be almost twice as much memory as would otherwise be required if the actual frame size is only 1 bit shorter than the standard frame size. Moreover, additional data transfer (re-arrangement) is needed because of the two-stage processing.
It would be desirable to improve upon the above mentioned scheme.